Charging liquid 407 by LP ? Where goes liquid ? can it damage the compressor ?

[pvl]

I went through all the questions about the charge with R407 or R410 and I find no answer on my question.
On the outdoor unit, there is only one service valve.And thats why there is something I do not understand.
I know I need to charge in liquid, and the compressor must not run. If I have to charge liquid through the low-pressure valve, where goes the liquid? do I need to do something to control that ? Can I turn on the compressor without the risk of damage? Should I start in heating or cooling mode to avoid this risk?
thank you for your help!!